1. Field of the Invention
The present invention relates to an objective perceptual video quality evaluation apparatus for automatically evaluating quality of a video, e.g., a received video image or a reproduced video image which is transmitted or accumulated after being subjected to an image processing such as compression coding without relying on subjective human judgment.
2. Description of the Related Art
There are conventionally known techniques related to the present invention as disclosed in, for example, ITU-T Recommendation J.143, “User requirements for objective perceptual video quality measurements in digital cable television” and ITU-T Recommendation J.144, “Objective perceptual video quality measurement techniques for digital cable television in the presence of a full reference”.
The ITU-T Recommendation J.143 mainly describes user requirements for automatic objective perceptual video quality measurements in television transmission. For the objective measurements, three frameworks of “Full Reference”, “Reduced Reference”, and “No Reference” are provided for, depending on how to use video signals before and after transmission. It is described how to apply one of the frameworks to a system according to purposes of use. For example, the “Full Reference” framework is generally to be used for measurement of quality of compression-coded video signal, and the “Reduced Reference” and “No Reference” frameworks are generally to be used for measurements of reception quality of a transmitted video signal. The ITU-T Recommendation J.143 there by shows user requirements for automatic objective perceptual video quality measurements.
The ITU-T Recommendation J.144 is a recommendation of “Pull Reference”-based automatic objective perceptual video quality measurements on the premise of a quality of a standard television video signal for secondary distribution. The “secondary distribution” refers to transmission of videos mainly between a television station and each viewer. As the other categories than the secondary distribution, primary distribution referring to delivery of program materials between television stations and material transmission for providing materials for such programs as sports and news programs are present. While the ITU-T Recommendation J.143 describes only the system frameworks, the ITU-T Recommendation J.144 describes specific techniques for quality measurements.
The “Full Reference”-based video quality measurement techniques disclosed in the ITU-T Recommendation J.144 attain the quality verified as the ITU recommendation. However, the techniques disclosed therein are based on the secondary distribution of video signals according to a standard television system. The standard television system means that with NTSC (525/60), a signal format is 720 pixels×486 lines and 30 frames per second (interlace scan mode) and with PAL (625/50), a signal format is 720 pixels×576 lines and 25 frames per second (interlace scan mode).
In case of the secondary distribution, bit rates allocated to the video compression coding, i.e., a television transmission band is assumed as about one to four Mbps. Furthermore, the available compression coding is mainly assumed as MPEG-2 scheme.
Meanwhile, as multimedia applications typified by those for IP broadcasting on the Internet and terrestrial digital one-segment broadcasting in the cellular telephone network have become popular, demand for evaluation of qualities of videos transmitted by these applications similarly to that of video qualities of television transmission videos rises.
As stated, the recommendation disclosed in the ITU-T Recommendation J.144 is on the premise of the television quality. Due to this, the techniques disclosed therein are incapable of ensuring high accuracy for videos obtained by compressing videos at low resolution and a low frame rate (e.g., 15 frames/second, 10 frames/seconds or 6 frames/second) using high compression coding such as MPEG-4/H.264 at low bit rate. Therefore, a technique for automatic objective perceptual video quality evaluation intended at these multimedia applications is desired.